Human aging is associated with glucose intolerance but the pathophysiologic mechanisms responsible are not known. Recently, in a study of MODY in the RW pedigree, we have demonstrated that measurement of insulin secretion and its pulsatility during prolonged glucose infusion can detect defects not identified by prior studies, specifically by the acute insulin response to glucose. We propose to study insulin fluctuations of young and elderly subjects during prolonged glucose infusion to see if we can discern any differences.